Would I be better off replacing the amp? or should I replace the speakers? Thinking of the Exile SX65Ms, but would my amp be too weak to drive them? Would definitely like some recommendations on speakers for my budget range.

Or...do I want to spend my $500-$600 and replace both the amp and the in boats?

Keep the original DX200.4 on your front pair @ 100WRMS per speaker
put a PPI p600.2 on your rear 2 pairs @ 150WRMS per speaker ($137)
Get 3 pairs of exile speakers for around $150 a pair ($450)
Your in for a touch under $600. You get everything

Since the Exiles are only 100rms, is there any advantage of going to the PPI 900.4 over the PPI p600.2?

If I went with Greeko's suggestion, since the p600.2 is a 2-channel amp I'd need to split the leads to serve the 4 speakers (1 pair at mid cabin, 1 pair at transom) ? Is it that simple?

Unfortunately I don't really have any more room on my board for a 4th amp (I didn't mention before that I currently have an amp pushing tower speakers and an amp pushing a sub). What are my options to totally replace the DX200.4 with a 6-channel amp? I'd need at least an amp with 600 total watts and 6 channels, right?

I have a 2 battery setup atm (1 house, 1 starter, perko/ASR). If I replace my DX or add, say, the 600.2 to my system, think that'll require me to add another battery? We do a lot of cove listening and I can currently run the system hard for at most 2-3 hours.

That amp is delivering about 25-35 watts per channel to the current speakers. The best money to be spent will be to upgrade the amp. A Kicker KXM400.4 will basically double your power. That would be one good choice. Your stock speakers are good units; they just want more power.

It will be better almost always to add power to any system first, then replace the speakers later if you want. Otherwise, you aer USUALLY adding higher-power-handling gear, while still under-powering it.

Thanks for your patience with me, i just dont get this stuff. I got 6 in boats, and each speaker will get wired to 1 of the 6 channels. There'll be no channels left, and I used up 150w x 6 = 900 watts, but it's a 1200 watt amp. What am I missing?

Since the Exile speakers are 100rms, wouldn't I want to push them with an amp that puts out at least 100rms per speaker?

What about running my 2 fronts with my current DX200.4, and then adding a Rockford Fosgate M600-4D or a XM15.4 - 800W (both are 100 watts x 4 channels @ 4) for the 4 main cabin speakers? Those amps are kinda pricey at around $450. Add in the 3 pairs of Exiles and I'd be looking at around $950. A little over the budget but what else is new. That would rock, yes?